The present invention relates to a machine for sealing containers by applying a covering film.
U.S. Pat. No. 4,974,392 in the name of the same Applicant, assumed included herein as reference, discloses a machine for closing containers by means of a sealing film, which substantially comprises a frame on which a conventional sealing head is located; said head applies the sealing film to the various containers, which are fed sequentially below the head.
In this patent, upstream of the sealing head there is an accumulation belt that moves intermittently so as to allow to prepare, upstream of the sealing head, a certain number of containers, which is a function of the size of said containers, before feeding all the containers below the sealing head by means of a pair of pusher arms with grip regions that simultaneously place below the sealing head the accumulated and positioned containers and remove from the sealing head the containers that have already been closed to place them on a removal conveyor.
This embodiment is particularly advantageous, since it allows the number of containers that can be accumulated to become practically independent of the pitch of the feeder conveyor, which corresponds to the maximum size of the containers that can be sealed by the apparatus.
With the arrangement disclosed in said patent, if one changes containers and works for example with smaller containers, the pitch, that is to say the distance between one container and the next, can be reduced, consequently increasing the number of containers that can be sealed fully and reducing the waste of sealing film.
This advantage is obtained by means of the accumulation conveyor, which advances intermittently, so as to gather a number of containers that increases if the size of the containers to be sealed decreases, so that the pusher arms, which are shaped according to the shape and number of the containers, can convey a larger number of closely arranged containers to the sealing station, reducing production time as well as the waste of sealing film.
This solution can be improved, especially as regards the elimination of downtimes: in the above described solution, the accumulation conveyor advances intermittently and in practice stops while waiting for the incoming containers.
It should be noted that in many cases the containers to be sealed contain liquid substances, and therefore it is necessary to use rather low acceleration values and perform speed changes very gradually in order to prevent spillage of the liquid present inside the containers.